The present invention generally relates to the manufacture of insulated structures and, in a preferred embodiment thereof, more particularly relates to water heater structures and associated manufacturing and insulation methods therefor.
A conventional water heater of either the electric or fuel-fired type normally comprises a water storage tank, typically of a metal construction, adapted to hold a quantity of pressurized, heated water for on-demand delivery to various plumbing fixtures such as sinks, tubs, showers, dishwashers or the like. Outwardly surrounding the tank is a jacket, typically of a metal construction, which defines around the tank a cavity which is filled with a suitable insulation material, usually a hardened foam insulation material which is initially injected into the cavity in liquid form during the fabrication of the water heater. Various control structures, such as thermostats and electric heating element structures project outwardly from the tank and are aligned with associated access openings in the jacket.
In order to shield these control structures from the insulation, and to prevent the insulation from being forced outwardly through the jacket access openings during the liquid insulation injection process, it is common practice to circumscribe the control structure areas within the tank/jacket cavity with insulation barriers commonly referred to as “foam dams”. One previously proposed method of providing a foam dam around a control structure projecting outwardly from a water heater tank, illustrated and described in U.S. Pat. No. 4,372,028 to Clark et al, is to provide a plastic bag having a peripherally sealed aperture extending therethrough, place the bag in the empty tank/jacket cavity with the aperture aligned with and circumscribing the control structure location, expanding the bag into sealing engagement with the tank and jacket by injecting foam insulation into the bag, and then permitting the injected foam to harden within the bag.
The empty remainder of the insulation cavity is then injected with additional liquid foam insulation which is prevented from encroaching into the control structure locations, or flowing outwardly through the associated jacket access openings, by the previously formed plastic bag-based foam dam. This second batch of injected liquid foam insulation contacts the periphery of the foam dam and hardens within the tank/jacket cavity to complete the tank insulation process.
Several well known problems, limitations and disadvantages are typically associated with this conventional plastic bag-based foam dam construction. First, after the second or main batch of foamed-in insulation hardens it tends to pull away from the plastic bag in a manner creating a gap between the second foam batch and the bag along the entire length of the water heater. This gap, caused by shrinkage of the second foam batch, undesirably permits appreciable heat loss from the tank therethrough.
Second, the current practice for filling the foam bag with the first batch of foam insulation is to inject a shot of foam into the bag and then let the injected foam “free rise” within the bag to fill it. This results in an undesirably decreased foam density in a top portion of the bag, resulting in a lesser insulation efficiency in the top portion of the bag.
Third, bags of this conventional type are typically of a flat construction, but are used to sealingly fill a three dimensional portion of the tank/jack insulation cavity. The result tends to be a filled bag with marginal foam coverage around the control or other structure around which the filled foam bag protectively extends.
As can readily be seen from the foregoing, a need exists for an improved plastic bag-based foam dam structure and related insulated tank apparatus and associated fabrication methods. It is to this need that the present invention is directed.